A panel of B-lymphoma cell lines is being used to stimulate class II restricted T-cell clones in an effort to biochemically characterize the events requisite for T-cell activation. We are investigating the interaction of a number of external stimuli that initiates a sequence of defined activation responses by these cloned T cells. The characterization of this model system will be used to identify the biochemical events that occur during the initial stages of an antigen-specific immune response to alloantigens and soluble foreign antigens. (CS)